I was having problems with my ignition amplifier getting hot and causing misfire.

So I moved the ignition amplifier away from the top of the engine and into the cabin of the car to stop it from overheating. This made things a lot better.

I bought two new coils from the market that matched the specs of the original coils. Now when I connect both coils in parallel, as per the wiring diagram, the ignition amplifier gets really hot! Hot enough not to be able to touch it, even though it's not now sitting on top of the hot engine. When I disconnect one of the coils, so the whole system is running only on one coil, the ignition amplifier only gets warm!!! What is the reason for this??? Now you can run the car on one coil but I feel that it sometimes stalls and also would not be able to run all 12 cylinders at high rpm.

I bought the single replacement coils as per the ones at SNG Barratts, but unfortunately when it got delivered I found it was faulty. So I found a coil of an old 90s V8 Mercedes which somewhat matches the specification of the single coil from SNG Barratts. Now with this coil the ignition amplifier gets hot, but not as hot as with the double coil setup.

Does anyone know how hot the ignition amplifier should get? Also how does the coil setup affect how hot the ignition amplifier get?

Thanks

 

The stock setup uses the intake manifold as part of the heatsink, as it is relatively cool when the engine is running. You need to ensure that the GM module inside the Lucas box has heatsink compound between it and the Lucas box base to help transfer heat. Wherever you mount the Lucas box, it should be attached to metal to help dissipate the heat. And yes, they do get hot.

 

The ignition amplifier is drawing about 6 amps of current so it does get hot. The reason it is on the intake manifold is it actually is a cool place, as all of the intake air is going through the manifold and it acts like a heatsink. The intake manifold is significantly cooler than the block, as there is no coolant going through it.

Wherever you have relocated the amp, make sure that it has a way of getting rid of the heat, and that it has a good electrical ground.

The earlier cars had 2 coils, wired in parallel. The reason was that low impedance coils were not redially available and by wiring in parallel that drops the effective resistance. Later V12 saloons changed to a single coil that was rated at about 0.5 ohms primary resistance. Any coil that is a modern low resistance coil should be able to work as a single coil.

Take a look at this description of how things work, you have the Constant Energy system: V12 IGNITION SYSTEMS / AJ6 Engineering

 

It is better to mount the amp in the airflow out in front of the radiator, for example:

 

My findings with these amps over too many cars and years.

The paste is critical, as mentioned.

Primary ohms is also out there on the critical list. Most module are OK up to 1.0-1.1. ohms, and at that they get HOT. Over that, stuff hits the fan real quick.

All my amps are mounted out the front of the radiator, near where the 2nd coil is, and are COOL to the touch at any time. The S3 has that amp under the passengers seat with a small computer fan cooling it, but since the A/C is always on, not an issue.

HT leads, all 13 of them, can cause resistance issues, age related mainly, and thus module heat.

Spark plug gap, critical on the HE at 0.025". Too wide, more resistance = heat.

These fancy spec spark lugs, YEH/NAH, the HE is not happy with them, so plain Jane spec sparkers are all that is needed

Rotor to cap "arc" height is another major issue.

Primary Ohm of the OE paired is 0.6, or close to. A standard modern coil of similar ohm will work just fine, as already mentioned.

 

Hi all

Quick question on the heatsink compound/paste that some of you have referred to. Is it the same thing used in computers to bond the heat sink to the CPU? Basically RTV silicon.

I have two types of RTV silicon, one is white in color and the other is grey/transparent type. Unfortunately the instructions are in Chinese so can't read them? Does anyone know which one to use?

Also do I just paste on the back of the module or do I need to completely cover it?

Thanks

 

RTV is an insulator, not a heatsink compound. You want something like Artic silver, or any good CPU heatsink paste available at a computer parts store. It just goes on the base of the GM HEI module inside the Lucas box. A small dab in the center will spread as it is bolted back down.

 

Hi there

We don't get many American brands here, mostly Chinese. Please check the pictures I've attached below, these are available here. Can you guess from the product code which would be the closest to Artic Silver?

Thanks

 

This sort of stuff: